The agreement will see the union buy up to 1.8 billion doses of the jab, making it the biggest single deal for a Covid-19 vaccine to date.
Fears have been growing in recent times over the safety of the AstraZeneca vaccine which is believed to cause rare, but potentially deadly, blood clots.
The European Commission announced the purchase during a visit to Pfizer’s manufacturing plant in Belgium, saying the vaccines will be used through to 2023.
The deal comes as pressure mounts on wealthy nations to stop hoarding vaccines to ensure there are enough available doses for developing countries.